Changing X coordinate appears not to work

I have a text field directly on a master page (there is a good reason for this) and I want to change it's X coordinate using Javascript code like this:

// directly call the "x" attribute

this.x = "200mm";

//  use a method call to change it

this.setAttribute ("200mm", "x");

I tried using events like initilalize, calculate, form:ready, form:layout, but the field won't move.

What is strange is that changing the field width works, using similar code:

// directly call the "w" attribute

this.w = "200mm";

//  use a method call to change it

this.setAttribute ("200mm", "w");

What am I missing? After some googling it appears these two fields ("x" for X coordinate and "w" for width) are pretty much alike.

I would be happy if someone could tell me if this works for him/her. At least I would now I haven't reached a dead end.

I'm using Lifecycle ES2 by the way.